1. Field of the Invention
This invention relates to a laser module. This invention particularly relates to a laser module, which comprises a laser element, a converging optical system for converging a laser beam having been radiated out from the laser element, and an optical fiber for receiving the laser beam having been converged by the converging optical system, the laser element and the converging optical system having been combined into a unit.
2. Description of the Related Art
So-called pig tail types of laser modules have heretofore been proposed. The proposed laser modules comprise a laser package, which is provided with a laser beam transmissive window for radiation of a laser beam and in which a laser element has been hermetically sealed, a converging optical system for converging the laser beam having been radiated out from the laser package, and an optical fiber for receiving the laser beam having been converged by the converging optical system, at least the laser package and the converging optical system having been combined into a unit.
By way of example, a laser module, wherein the laser package and the converging optical system have been accommodated in an identical holder, and wherein an end section of the optical fiber on the laser beam incidence side is also accommodated within the holder, has been disclosed in, for example, Japanese Unexamined Patent Publication No. 2004-288879. Also, a laser module, wherein the laser package and the converging optical system have been accommodated respectively in different holders, wherein the holder accommodating the laser package and the holder accommodating the converging optical system have been welded to each other, and wherein a receptacle for receiving the end section of the optical fiber on the laser beam incidence side has been fitted to the holder accommodating the converging optical system, has been disclosed in, for example, Japanese Unexamined Patent Publication No. 7(1995)-168064.
From the view point of the easiness of the welding of members to each other, general-purpose properties, and the like, ordinarily, a stainless steel (SUS304) has heretofore been utilized as the material of the aforesaid holder. The stainless steel (SUS) has a comparatively low thermal conductivity of approximately 16 W/mK. By virtue of the low heat diffusing characteristics, the stainless steel is appropriate for the welding operation.
As the laser element, a laser element having a comparatively low output power, such as an infrared semiconductor laser element, which produces a laser beam having a wavelength of 980 nm and has an output power of 90 mW, has heretofore been utilized. An electric power-to-laser beam conversion efficiency of the infrared semiconductor laser element is estimated to fall within the range of 40% to 60%, and the quantity of heat released from the laser element at the time of the output power of 90 mW is estimated to fall within the range of 60 mW to 135 mW.
Recently, it is studied to utilize an ultraviolet semiconductor laser element (i.e., a broad area semiconductor laser element), such as a GaN type of an ultraviolet semiconductor laser element, which has a high output power, e.g. an output power falling within the range of 200 mW to 500 mW, as the aforesaid laser element. The electric power-to-laser beam conversion efficiency of the ultraviolet semiconductor laser element, such as the GaN type of the ultraviolet semiconductor laser element, is estimated to fall within the range of 20% to 25%, and the quantity of heat released from the laser element at the time of the output power of 500 mW is estimated to fall within the range of 1.5 W to 2 W. The quantity of heat released from the ultraviolet semiconductor laser element is approximately five to six times as large as the quantity of heat released from the infrared type of the semiconductor laser element. Therefore, in cases where the holder made from the stainless steel (SUS304) having the low thermal conductivity is utilized, the heat released from the ultraviolet semiconductor laser element is not capable of being dissipated sufficiently.
Also, regardless of the types of the laser elements, in the cases of a beam combining type of module utilizing a laser package, in which a plurality of laser elements have been hermetically sealed, as the number of the laser elements becomes large, the total heat release quantity within the laser package becomes large. Therefore, in cases where the holder made from the stainless steel (SUS) having the low thermal conductivity is utilized, the heat released from the laser elements is not capable of being dissipated sufficiently.
If the heat released from the laser element is not capable of being dissipated sufficiently, the problems will occur in that the life time of the module becomes short due to thermal deterioration of the laser element, and the like. In, for example, Japanese Unexamined Patent Publication No. 2004-288879, a heat dissipating structure, in which the heat dissipation is performed with a temperature control unit, such as a Peltier element, fitted to a laser package, is described as the related art. Also, in, for example, Japanese Unexamined Patent Publication No. 2004-288879, there is disclosed a heat dissipating structure, wherein a stem (2), which is made from a material having good thermal conduction characteristics, such as CuW, and which has an L-shaped cross-section, is fitted to a laser package, and wherein the heat dissipating characteristics are enhanced without a temperature control unit being utilized.
However, with the conventional techniques, in which the temperature control unit or the stem (2) having the L-shaped cross-section is fitted to the laser package in order for the heat dissipating characteristics to be enhanced, the problems occur in that the number of parts is not capable of being kept small, the cost is not capable of being kept low, and the size of the module is not capable of being kept small.
Also, in, for example, Japanese Unexamined Patent Publication No. 7(1995)-168064 disclosing the laser module, wherein the laser package and the converging optical system have been accommodated respectively in different holders, and wherein the holder accommodating the laser package and the holder accommodating the converging optical system have been welded to each other, nothing is disclosed with respect to a heat dissipating structure to be utilized in cases where a high output power laser element is utilized.